Heretofore, operation of microwave radiometers has generally severely degraded during precipitation events because of contamination of the radiometer antenna system by hydrometeors (precipitation particles in liquid, ice, or mixed or wetted phase). Hence, microwave radiometer measurements have not provided meaningful or useful data when made during precipitation events, primarily because liquid water and/or other precipitation products or contaminants on the dielectric window of the antenna system causes erroneously high measurement values. This inability to operate accurately during precipitation events has caused discontinuity of meteorological measurements and inhibited use of microwave radiometers for determination of parameters such as precipitation rates, duration and event location relative to the antenna.
Radiometers have been used for present weather measurements and have been used to feed predictive models on an experimental basis. However, to date, the reliability and accuracy of radiometers during all weather conditions has proven insufficient thereby disqualifying such instruments for significant use as operational weather observation systems. This deficiency has again been primarily due to the contamination of observations due to precipitation on the antenna system, as well as inadequacy in modeling high liquid content during very wet or precipitating conditions, and inadequacy in modeling scattering of microwave radiation from hydrometeors. Therefore, use of microwave radiometers has often been limited to field observation during nonprecipitating periods (or, at best, where conditions of extremely light moisture may be present on the antenna window).
Accouterments for such radiometers have been used or suggested for promoting quick drying of the antenna system after it has become wet, but have not addressed the issues of actual use of the radiometer or other such instrument during precipitation events. One heretofore known device employs a rapidly spinning reflector to throw off precipitation products. This approach, while utilized, has proven problematical due to further contamination from spray and mist created by the system during precipitation events.
It has also been known heretofore to utilize a relatively light air flow from an axial flow fan after a precipitation event to more quickly dry the antenna system (i.e., “dew blowers” used to promote more rapid evaporation of moisture at the antenna window; see U.S. Pat. No. 5,526,676). Systems utilizing light air flow are not, however, intended for use during precipitation events, nor are they effective during such events to enable accurate readings by the radiometer. Moreover, such heretofore known or utilized air flow systems have not been effective across the entire dielectric window (drying the top only while neglecting the sides of the window). Axial flow fans employed by such systems have caused vorticity in the flow, inducing problems at the dielectric window associated with such nonlaminar flow, have been susceptible to back pressure, and have been implemented so that precipitation may be passed through the system and back onto the antenna window.
Use of hydrophobic surface films at the dielectric window have also been heretofore suggested and/or utilized for promotion of beading and runoff of liquid water (see, for example, U.S. Pat. No. 4,873,481). Such hydrophobic surface treatments alone, however, have not proven to be entirely satisfactory.